Traditionally, a nickel hydride battery has been primarily used as a fuel battery for an automobile but, in recent years, the adoption of a lithium-ion battery that has been used in a portable phone, a personal computer, or the like is considered because of a light weight and a high operating voltage.
A lithium-ion battery constitutionally gives functions as an electrode to a battery case including a body and a lid and an aluminum material of a high electrical conductivity is used as the battery case material. Further, an aluminum material can withstand deep drawing and hence can be used for producing a square or round container for a battery case through a forming process.
When a battery is used alone in a portable phone or the like, a strong AA3000-series aluminum alloy is used for the body and the lid of a battery case in order to prevent swelling. A battery case of this kind is bonded by applying laser welding to the body and the lid, both comprising an aluminum alloy material, along the periphery of the lid.
Patent Documents 1 and 2 disclose a method for producing a battery case by: interposing a brazing material having a lower melting point than an aluminum alloy material at the joint interface between the case main body and the lid, both comprising an A3003 aluminum alloy; and bonding the joint interface by solid-phase diffusion bonding of the aluminum material.
Patent Document 3 discloses a battery case the corrosion resistance of which is improved by forming a film of synthetic-resin paint, a film of ceramic coating, or a film of aluminum oxide coating on the outer surface of the battery case made of aluminum or an aluminum alloy.
Patent Document 4 discloses a method for producing a lithium-ion secondary battery by bonding a lid comprising a JIS-A3003 aluminum alloy to the opening of a closed-end square-tube-shaped outer case comprising the JIS-A3003 aluminum alloy by laser welding. Here, Patent Document 4 further describes a JIS-A1050 aluminum material as a material for a battery case.    Patent Document 1: JP-A 180438/1998 (H10)    Patent Document 2: JP-A 11964/2000    Patent Document 3: JP-A 106152/2000    Patent Document 4: JP-A 123822/2000